#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
using namespace std;

class Solution {
public:
    class Sum
    {
    public:
        Sum()
        {
            _ret += _i;
            _i++;
        }
    };

    int Sum_Solution(int n) {
        Sum arr[10];

        return _ret;
    }
private:
    static int _i;
    static int _ret;

};
int Solution::_i = 1;
int Solution::_ret = 0;

int main()
{
    int n = 0;
    scanf("%d", &n);
    Solution ret;
    printf("%d",ret.Sum_Solution(n));
}

